Field of the Invention
The present disclosure relates to an apparatus for touch sensor test, and more particularly, to an apparatus capable of checking whether there is short between electrodes of touch sensor, regardless of an amount of capacitance, fast and simply.
Discussion of the Related Art
A touch sensor is an input device capable of sensing a physical contact from user's finger or other objects and changing the physical contacts with a corresponding electric signal, in order to recognize coordinates (the location of a point in space) or user's gesture. The touch sensor is widely applicable to electric devices or systems. Particularly, when the touch sensor is associated for a display device, the touch sensor may be substituted with an additional input device such as a keypad which occupies some space in an electric device or system. Accordingly, the touch sensor can be used in a mobile phone, a smart phone, a personal digital assistant (PDA), a tablet personal computer, and the like.
According to a method for sensing touch or contact, the touch sensor types may include a 5-wire (or 4-wire) resistive, surface capacitive, projected capacitive, surface acoustic wave and Infrared sensors. Among those, the surface capacitive sensors are activated with the touch of object, e.g., human finger/skin or a stylus, holding an electrical charge. When exposed finger touches the monitor screen, a transparent electrode film placed on top of the glass panel reacts to the static electrical capacity of the object. The change in capacitance is detected by sensors located at the four corners of the screen. The monitor screen including the surface capacitive sensors may have advantages of durability, high scratch resistance, high integration (thin screen), multi-touch support, and so on.
Two electrodes of the touch sensor are separate from each other via an insulator electrically. However, the two electrodes may be shorted with some resistance, not electrically separate, because of some reasons such as incomplete etching on manufacturing process. These defects can be detected by a test circuit including a current source. The test circuit detects an amount of current and a corresponding resistance incurred to determine whether two electrodes are electrically shorted when the current is supplied into each touch sensor.
In the test circuit, the amount of current supplied from the current source is increased until a predetermined value is outputted. Then, the amount of supplied current can be used to determine whether there is electric short between two electrodes of the touch sensor. However, the amount of supplied current from the test circuit can be changed because of resistance between the two electrodes as well as capacitance of the two electrodes. Not every touch sensor has the same capacitance. Accordingly, the test circuit may easily detect resistance between two electrodes, which is closer to 0Ω (for example, two electrodes are electrically short and resistance is minimized). However, it is hard for the test circuit to determine whether the touch sensor is defective when its resistance between any two electrodes is a few-hundreds kΩ to a few MΩ.